Polyelectrolyte Multilayer Films Research Articles

Effect of the silicon carbide nanoparticles introduction on biological properties of porous polymer coatings

The multilayer polyelectrolyte films (PEMs) seem to be a promising material to reconstruct the structure and behavior of the extracellular matrix.

Saline-enabled self-healing of polyelectrolyte multilayer films

After introducing a third polyelectrolyte, the healing ability of polyelectrolyte multilayer film fabricated by LbL technique is largely enhanced, and can undergo rapid healing of several tens of micrometer-sized cuts when exposed to normal saline.

Dynamic stiffness of polyelectrolyte multilayer films based on disulfide bonds for in situ control of cell adhesion.

The stiffness of the substrates has been found to have a strong effect on cell behaviors, especially on cell adhesion, which is the first cellular event when cells contact materials. Much effort has been made to develop the materials with controlled stiffness for regulating cell adhesion. However, most available strategies for controlling the stiffness of material surfaces are generally limited to be static, which means that the stiffness is fixed during cell adhesion. Herein, we developed polyelectrolyte multilayer films (PEMs), and their stiffness can be dynamically modulated by mild stimuli. The PEMs were made by alternative deposition of poly-l-lysine (PLL) and thiol group modified hyaluronan (HA-SH) using the layer-by-layer assembly technique. The (PLL/HA-SH) multilayers can be cross-linked via oxidation of thiol groups. After crosslinking, the stiffness was increased and the adhesion of fibroblast cells was promoted. The stiffness of the multilayer films can be down-regulated dynamically by adding glutathione (GSH) in the medium, leading to in situ reduction of cell adhesion. Our study provides a promising strategy for the development of material surfaces with dynamically changeable stiffness, which is of great potential in the field of cell-based biomaterials.

Biomimetic niche for neural stem cell differentiation using poly-L-lysine/hyaluronic acid multilayer films.

Polyelectrolyte multilayer films have been suggested as tunable substrates with flexible surface properties that can modulate cell behavior. However, these films' biological effects on neural stem/progenitor cells have rarely been studied. Herein, biomimetic multilayer films composed of hyaluronic acid and poly-L-lysine were chosen to mimic the native extracellular matrix niche of brain tissue and were evaluated for their inductive effects, without the addition of chemical factors. Because neural stem/progenitor cells are sensitive to substrate properties, it is important that this system provides control over the surface charge, and slight stiffness variations are also possible. Both of these factors affect neural stem/progenitor cell differentiation. The results showed that neural stem/progenitor cells were induced to differentiate on the poly-L-lysine/hyaluronic acid multilayer films with 0.5-4 alternating layers. In addition, the neurite outgrowth length was regulated by the surface charge of the terminal layer but did not increase with the layer number. In contrast, the quantity of differentiated neurons was enhanced slightly as the number of layers increased but was not affected by the surface charge of the terminal layer. In sum, material pairs in the form of native poly-L-lysine/hyaluronic acid films achieved important targets for neural regenerative medicine, including enhancement of the neurite outgrowth length, regulation of neuron differentiation, and the formation of a network. These extracellular matrix-mimetic poly-L-lysine/hyaluronic acid multilayer films may provide a versatile platform that could be useful for surface modification for applications in neural engineering.

Development of Decellularized Aortic Valvular Conduit Coated by Heparin–SDF-1α Multilayer

Decellularization can reduce the immune response to aortic valve allograft tissue, but the thrombogenicity and in vivo remolding of these grafts remain controversial. The aim of the present study was to modify the surface of decellularized valvular conduits with heparin-stromal cell-derived factor-1α (SDF-1α) polyelectrolyte multilayer film and to test the thrombogenicity and biocompatibility in vitro and recellularization in vivo. The donor aortic valvular conduits were decellularized with a combination of different detergents and were coated with heparin and SDF-1α alternately to form a polyelectrolyte multilayer. Platelet adhesion and lactate dehydrogenase assay were used to evaluate the antiplatelet property. The adhesion, growth, and migration of bone marrow stem cells (BMSCs) to the scaffolds were assessed. For in vivo studies, the grafts were anastomosed to the infrarenal aorta, without or with heparin and SDF-1α multilayer. Functional assessment was performed by Doppler echography and micro-computed tomography at 2-week and 4-week time points after implantation. Explanted grafts were examined histologically and by immunohistochemistry. In vitro studies demonstrated that the heparin-SDF-1α multilayer film improved hemocompatibility with respect to a substantial reduction of platelet adhesion. BMSCs also achieved better adhesion, proliferation, and migration on the modified graft. For in vivo studies, the grafts in both groups remained patent after 4 weeks, but it was demonstrated that the modified decellularized grafts had better self-endothelialization and recruitment of endothelial progenitor cells. These results indicate that heparin-SDF-1α multilayer film can be used to cover the decellularized aortic valvular graft to decrease platelet adhesion while precipitating regeneration of the decellularized aortic valve allograft in vivo.

Comparison of permeability of poly(allylamine hydrochloride)/and poly(diallyldimethylammonium chloride)/poly(4-styrenesulfonate) multilayer films: Linear vs. exponential growth

The ability to form highly tailored polymer thin films with various functional groups or nanoobjects incorporated in the film structure is the main reason of a popularity of the Layer-by-Layer method. In the present paper we concentrated on the formation and permeability of multilayer polyelectrolyte films exhibiting various growth regimes, linear and exponential. Films were formed of two model pairs of polyelectrolytes: poly(allylamine hydrochloride)/poly(4-styrenesulfonate) (PAH/PSS) and poly(diallyldimethylammonium chloride)/poly(4-styrenesulfonate) (PDADMAC/PSS) at various ionic strengths of polyelectrolyte solutions. Quartz crystal microbalance with dissipation (QCM-D) was used to determine the films’ mass and viscoelastic properties in situ. The results concerning the films growth were compared with the thickness in “dry” state measured by ellipsometry. The Electrochemical Impedance Spectroscopy (EIS) with the redox couple potassium hexacyanoferrate (II) and (III) was used to determine the electrochemical impedance of films deposited at gold rotating disk electrode (RDE). The measurements showed that the obtained ellipsometric thickness, mass and resistance of multilayer films depended on the number of deposited polyelectrolyte layers and the ionic strength of PE solutions. However, PAH/PSS films formed at high ionic strength, exhibiting linear growth had much higher impedance than much thicker PDADMAC/PSS films with the exponential growth. We attributed that effect to the more “spongy” structure of exponentially growing films, containing more water.

Fabrication and Characterization of Ferrocene-Derived Sensor for Hydrogen Peroxide Detection

Ferrocene (Fc) is an organometallic compound of sandwich structure. As the anticancer and excellent electrical activities, ferrocene and its derivatives have many applications in electrochemical monitoring [1-3]. Hydrogen peroxide (HP), with strong permeability and oxidation properties, is the product of many peroxidase catalyzed reaction, and it is widely used in medical and cosmetic fields, even for food bleaching by some illegal merchants which may cause healthy problem. In this study, the polyelectrolyte multilayer films containing ferrocene-derived polymer assembling by sol-gel process [4] was introduced to HP determination as a sensor.

Label-free selection and enrichment of liver cancer stem cells by surface niches build up with polyelectrolyte multilayer films

Recent studies indicate that a small population of cancer cells exhibits stem cell properties and are referred to as cancer-initiating or cancer stem cells (CSCs). The selection and identification of cancer stem cells through methods require well-defined biomarkers and immunolabeling procedures are complicated and often unreliable. Herein, we fabricated a series of microenviroment by using polyelectrolyte multilayers (PEM) nanofilms to program and mimic hepatocellular carcinoma CSCs niches for CSCs selection with a label-free method. When cultured on PEM substrates, human cancer cell lines-Huh7 cells grew into individual round colonies and these cells displayed high marker expression of CSCs. Especially, these selected cells demonstrated significant chemo-resistant property in comparison with normal population. Therefore, we believed that niches selection and colony formation method may provide a new strategy on CSCs selection and drug evaluation for cancer therapy.

Successful differentiation of neural stem/progenitor cells cultured on electrically adjustable indium tin oxide (ITO) surface.

In order to control differentiation of neural cells and guide the developed neurites to targets, polyelectrolyte multilayer (PEM) films were used because of their capability of modulation of electrical charged characteristics, thickness, and stiffness. In this work, we suggested that indium tin oxide (ITO) is an alternative surface to achieve the above-mentioned objectives. A microfluidic system with four culture chambers was developed and each chamber consisted of parallel ITO surfaces for the application of adjustable electrical field. Neural stem/progenitor cells (NSPCs) were respectively cultured on the ITO surfaces with and without PEM film, constructed by alternate adsorption of poly(L-lysine) (PLL) and poly(L-glutamic acid) (PLGA). Analyses of cell morphology, cytotoxicity, process outgrowth, differentiated cell types, and neuron functionality were compared between both surfaces. In this study, NSPCs successfully differentiated on ITO surface with electrical stimulation. The optimal electrical potential was found to be 80 mV that could stimulate the longest process, i.e., >300 μm, after 3 days culture. Cell differentiation, process development, and functionality of differentiated neuron on ITO surface were shown to be strongly controlled by the electrical stimulation that can be simply adjusted by external equipment. The electrically adjustable cell differentiation reported here could potentially be applied to neurochip for the study of neural signal transmission in a well-constructed network.

Graphene improved electrochemical property in self-healing multilayer polyelectrolyte film

• bPEI/(PAA-GE) self-healing multilayer polyelectrolyte film was prepared by poly(acrylic acid) (PAA), graphene(GE) and branched poly(ethyleneimine) (bPEI) based on LBL self-assembly technique. • The bPEI/(PAA-GE) self-healing multilayer polyelectrolyte film shows excellent self-healing ability. • The bPEI/(PAA-GE) film has an improved conductive than bPEI/PAA multilayer polyelectrolyte film. Mimicking the nature to confer synthetic materials with self-healing property in order to expand their lifespan is highly desirable and has attracted much more attention from the scientific community. But poor electrochemical property of the fabricated self-healing materials limit the current and future application. Here, self-healing multilayer polyelectrolyte film based on branched poly(ethyleneimine) (bPEI), poly(acrylic acid) (PAA) and graphene(GE) (bPEI/(PAA-GE)) was prepared by layer-by-layer (LBL) self-assembly technique. The bPEI/(PAA-GE) self-healing multilayer polyelectrolyte film not only shows excellent self-healing ability at high humidity, but also possesses good electrical conductivity. It is promised to be applied in battery, supercapacitor or hydrogen fuel cell to improve their cyclic stability and lifetime.

Facile formation of nanoparticle patterns by water induced flow of a polymer thin film

In general, techniques of particle arrays on polyelectrolyte multilayers involve complex and inefficient steps. Here, we present a simple yet robust method for fabricating ordered two-dimensional nanoparticle arrays on polyelectrolyte multilayers via water induced flow of multilayer films. The process is easy and repeatable without the requirement of complicated surface preparation or chemical modification. By droplet evaporation of silica or other functional nanoparticle solutions on a patterned PDMS stamp, nanoparticle arrays on polyelectrolyte multilayer film surfaces will occur when the PDMS stamp contacts with polyelectrolyte multilayers. This work provides a facile and efficient approach to fabricate colloidal nanoparticle or other functional nanoparticle arrays on polyelectrolyte multilayers which are potentially useful for sensor materials, biomaterials and so on.

Shear induced changes in the streaming potential of polyelectrolyte multilayer films

Streaming potential measurement is one of the most frequently used characterization methods of polyelectrolyte multilayer films. In most cases, the adsorption of a polyelectrolyte occurs up to an overcompensation of the surface charge. Herein, we generalize previous findings that the obtained streaming potential (transformed into a relative ζ potential) is dependent on the history of the measurement and in particular that shear stresses due to the flow of the solution induce a reduction in the absolute values of the ζ potential. These findings show that huge care should be taken when defining an experimental protocol aimed to measure the zeta potential of polyelectrolyte multilayer films using the streaming potential method. Ideally, to avoid the influence of shear induced desorption of polyelectrolytes on the zeta potential values, polyelectrolyte multilayer films made from different number of layers should be characterized independently under overall identical conditions.

Controllably local gene delivery mediated by polyelectrolyte multilayer films assembled from gene-loaded nanopolymersomes and hyaluronic acid.

To explore a spatiotemporally controllable gene delivery system with high efficiency and safety, polyelectrolyte multilayer (PEM) films were constructed on titanium or quartz substrates via layer-by-layer self-assembly technique by using plasmid deoxyribonucleic acid-loaded lipopolysaccharide–amine nanopolymersomes (pNPs) as polycations and hyaluronic acid (HA) as polyanions. pNPs were chosen because they have high transfection efficiency (>95%) in mesenchymal stem cells (MSCs) and induce significant angiogenesis in zebrafish in conventional bolus transfection. The assembly process of PEM films was confirmed by analyses of quartz crystal microbalance with dissipation, X-ray photoelectron spectroscopy, infrared, contact angle, and zeta potential along with atomic force microscopy observation. Quartz crystal microbalance with dissipation analysis reveals that this film grows in an exponential mode, pNPs are the main contributor to the film mass, and the film mass can be modulated in a relatively wide range (1.0–29 μg/cm2) by adjusting the deposition layer number. Atomic force microscopy observation shows that the assembly leads to the formation of a patterned film with three-dimensional tree-like nanostructure, where the branches are composed of beaded chains (pNP beads are strung on HA molecular chains), and the incorporated pNPs keep structure intact. In vitro release experiment shows that plasmid deoxyribonucleic acid can be gradually released from films over 14 days, and the released plasmid deoxyribonucleic acid exists in a complex form. In vitro cell experiments demonstrate that PEM films can enhance the adhesion and proliferation of MSCs and efficiently transfect MSCs in situ in vitro for at least 4 days. Our results suggest that a (pNPs/HA)n system can mediate efficient transfection in stem cells in a spatially and temporally controllable pattern, highlighting its huge potential in local gene therapy.

Porous PLGA microspheres tailored for dual delivery of biomolecules via layer-by-layer assembly.

Tissue engineering is a complex and dynamic process that requires varied biomolecular cues to promote optimal tissue growth. Consequently, the development of delivery systems capable of sequestering more than one biomolecule with controllable release profiles is a key step in the advancement of this field. This study develops multilayered polyelectrolyte films incorporating alpha-melanocyte stimulating hormone (α-MSH), an anti-inflammatory molecule, and basic fibroblast growth factor (bFGF). The layers were successfully formed on macroporous poly lactic-co-glycolic acid microspheres produced using a combined inkjet and thermally induced phase separation technique. Release profiles could be varied by altering layer properties including the number of layers and concentrations of layering molecules. α-MSH and bFGF were released in a sustained manner and the bioactivity of α-MSH was shown to be preserved using an activated macrophage cell assay in vitro. The system performance was also tested in vivo subcutaneously in rats. The multilayered microspheres reduced the inflammatory response induced by a carrageenan stimulus 6 weeks after implantation compared to the non-layered microspheres without the anti-inflammatory and growth factors, demonstrating the potential of such multilayered constructs for the controlled delivery of bioactive molecules.

Polyelectrolyte multilayer electrostatic gating of graphene field-effect transistors.

We apply polyelectrolyte multilayer films by consecutive alternate adsorption of positively charged polyallylamine hydrochloride and negatively charged sodium polystyrene sulfonate to the surface of graphene field effect transistors. Oscillations in the Dirac voltage shift with alternating positive and negative layers clearly demonstrate the electrostatic gating effect in this simple model system. A simple electrostatic model accounts well for the sign and magnitude of the Dirac voltage shift. Using this system, we are able to create p-type or n-type graphene at will. This model serves as the basis for understanding the mechanism of charged polymer sensing using graphene devices, a potentially technologically important application of graphene in areas such as DNA sequencing, biomarker assays for cancer detection, and other protein sensing applications.

Stimuli-responsive controlled release and molecular transport from hierarchical hollow silica/polyelectrolyte multilayer formulations.

The smart designing of polymer hybrid carriers with a selective property will play a pivotal role in improving patient care and simplifying treatment regimes in the clinic. The controlled drug release of biomolecules from thin film coatings provides a simple pathway to offer complex localized in vivo dosing. In this investigation, we showed that it is possible to take advantage of the structure of hierarchically structured hollow silica/polymer hybrid system to control drug release. Drug-loaded polyelectrolyte multilayer films were developed using layer-by-layer assembly, incorporating the surface of the hierarchically structured hollow silica spheres. In comparison to the conventional hollow silica system, the synthesized formulation exhibited an enhanced stability, higher drug loading and better residual capacity of biomolecules. This rationally integrated architecture was demonstrated to be a very effective and controllable carrier for the drug release by changing the pH value. In addition, the developed system presented a highly selective molecular transport of doxorubicin hydrochloride (DOX), a model anti-cancer agent, at different pH values; moreover, it could be further applied to tailor cell viability, making it more promising for advanced drug therapy.

Assembly of polyelectrolyte multilayer films on supported lipid bilayers to induce neural stem/progenitor cell differentiation into functional neurons.

The key factors affecting the success of neural engineering using neural stem/progenitor cells (NSPCs) are the neuron quantity, the guidance of neurite outgrowth, and the induction of neurons to form functional synapses at synaptic junctions. Herein, a biomimetic material comprising a supported lipid bilayer (SLB) with adsorbed sequential polyelectrolyte multilayer (PEM) films was fabricated to induce NSPCs to form functional neurons without the need for serum and growth factors in a short-term culture. SLBs are suitable artificial substrates for neural engineering due to their structural similarity to synaptic membranes. In addition, PEM film adsorption provides protection for the SLB as well as the ability to vary the surface properties to evaluate the effects of physical and mechanical signals on NSPC differentiation. Our results revealed that NSPCs were inducible on SLB-PEM films consisting of up to eight alternating layers. In addition, the process outgrowth length, the percentage of differentiated neurons, and the synaptic function were regulated by the number of layers and the surface charge of the outermost layer. The average process outgrowth length was greater than 500 μm on SLB-PLL/PLGA (n = 7.5) after only 3 days of culture. Moreover, the quantity and quality of the differentiated neurons were obviously enhanced on the SLB-PEM system compared with those on the PEM-only substrates. These results suggest that the PEM films can induce NSPC adhesion and differentiation and that an SLB base may enhance neuron differentiation and trigger the formation of functional synapses.

Hyaluronic acid/poly‐L‐lysine multilayers coated with gold nanoparticles: cellular response and permeability study

Polyelectrolyte multilayer films have been widely studied over the past decade for bioapplications due to their proven reservoir properties for proteins and peptides, growth factors, nucleic acids, drugs, etc. Thick (micrometer‐sized) and soft multilayer films made of biopolymers possess high reservoir capacity but are usually cell repellent. Recently, a new approach has been developed based on physical modification of the films made from hyaluronic acid (HA) and poly‐L‐lysine (PLL) by coating film surface with gold nanoparticles (AuNP). This allows stiffening of the soft HA/PLL film, but still keeps the main part of the film intact to ensure its reservoir ability. Here we have studied cellular adhesion and permeability of the AuNP‐coated films. Different cell types (neuronal SH‐SY5Y, L929 fibroblasts, human embryonic kidney HEK 293 cells, and cervical cancer HELA cells) have been examined. Film free regions formed by mechanical scratching have been used as controls for cellular adhesion. For the permeability study small dye carboxyfluorescein (CF) and large macromolecule (PLL) have been utilized. As found in this study, (HA/PLL)24 films are cell repellent for all considered cell lines. But an improved adhesion to the AuNP‐coated films has been observed for all the cells lines except of HEK. AuNP coating leads to formation of a kind of semipermeable layer on the film surface, which allows small molecules such as CF to diffuse fast into the film, while diffusion of large molecules (PLL) is hindered. Being cell adhesive and selectively permeable AuNP‐coated multilayer films could serve as a novel platform for film‐mediated controlled drug delivery. Copyright © 2014 John Wiley & Sons, Ltd.

Cellular response to titanium discs coated with polyelectrolyte multilayer films

The purpose of this study was to investigate the effects of polyelectrolyte multilayer (PEM) coatings on the biological behavior of titanium (Ti) substrates. Collagen type Ι/hyaluronic acid (Col/HA) and chitosan/hyaluronic acid (Chi/HA) multilayer PEM coatings were introduced onto Ti substrates using layer-by-layer assembly. Contact angle instruments and quartz crystal microbalance were used for film characterization. The results obtained showed that both Col/HA and Chi/HA surfaces had high hydrophilicity and promoted cell adhesion in MC3T3-E1 pre-osteoblast and human gingival fibroblast cells. In addition, the synthesis of function-related proteins and gene expression levels in both MC3T3-E1 and fibroblast cells was higher for the Col/HA coating compared with the Chi/HA coating, indicating better cellular response to the Col/HA coating.

In vitro studies on regulation of osteogenic activities by electrical stimulus on biodegradable electroactive polyelectrolyte multilayers.

In this study, a novel electroactive tetreaniline-containing degradable polyelectrolyte multilayer film (PEM) coating [(poly(l-glutamic acid)-graft-tetreaniline/poly(l-lysine)-graft-tetreaniline)n, (PGA-g-TA/PLL-g-TA)n] was designed and fabricated by layer-by-layer (LbL) assembly method. Compared with the nongrafted PEMs, the tetreaniline-grafted PEMs showed higher roughness and stiffness in micro/nanoscale structures. The special surface characteristics and the typical electroconductive properties were more beneficial for adhesion, proliferation, and differentiation of preosteoblast MC3T3-E1 cells. Moreover, the enhanced effects were observed on the modulation of MC3T3-E1 cells that differentiated into maturing osteoblasts, when the electroactive PEMs were coupled with electrical stimulus (ES), especially in the early phase of the osteoblast differentiation. The alkaline phosphatase (ALP) activity, calcium deposition, immunofluorescence staining, and RT-qPCR were evaluated on the differentiation of preosteoblast. These data indicate that the comprehensive effects through coupling electroactive scaffolds with electrical stimulus are better to develop bioelectric strategies to control cell functions for bone regeneration.